Targeting cefuroxime plasma concentrations during coronary artery bypass graft surgery with cardiopulmonary bypass.

BACKGOUND: Patients are at risk for severe postoperative infections after coronary artery bypass graft (CABG) surgery. Clinical laboratory data showed that unbound plasma concentrations of cefuroxime were not always adequate, therefore we developed a new dosing regimen. OBJECTIVE: The aim of this prospective study is to evaluate the new dosing strategy by monitoring patients for unbound cefuroxime plasma concentrations during CABG surgery with cardiopulmonary bypass (CPB). SETTING: A Dutch teaching hospital. METHODS: In this prospective trial, patients scheduled for CABG surgery with CPB were included. A starting dose of 1500 mg cefuroxime was given with anesthesia induction, followed by 750 mg cefuroxime every hour until wound closure. In case of renal failure the dosing regimen was adapted. Serial blood samples were collected before, during and after the CPB process. Pharmacokinetic modelling was performed by using an 'iterative two-stage Bayesian population procedure'. MAIN OUTCOME MEASURE: Unbound plasma concentrations of cefuroxime. RESULTS: 22 patients were included, data could be evaluated of 21 patients. In 24 % of the patients the unbound cefuroxime plasma concentration was below the target range during surgery before CPB started. Patients with a bodyweight above 100 kg or age <60 years were more likely to have unbound plasma concentrations below the target range (P = 0.030 and P = 0.008). During CPB, the half-life of unbound cefuroxime increased by 17 % and the clearance decreased by 11 % compared to before CPB (P = 0.033 and P = 0.014). The mean pharmacokinetic parameters before, during and after CPB were as follows: elimination half-life 72, 84 and 76 min; clearance of unbound cefuroxime (Clu) 14.2, 12.7, 13.8 l/h and volume of distribution (Vu) 0.280, 0.284 and 0.290 l/kg respectively. Variations in unbound fractions before, during and after CPB were below 2 %, implicating the unbound fraction of cefuroxime is not influenced by CPB. CONCLUSION: Our results show that CPB during CABG surgery does not lead to inadequate unbound cefuroxime concentrations. Age, renal function and possibly also weight are more important factors that can result in unbound plasma cefuroxime concentrations below the target value.

Blood concentrations of cefuroxime in cardiopulmonary bypass surgery.

OBJECTIVES: Patients with coronary artery bypass graft (CABG) surgery are at risk for severe postoperative infections. Prophylactic cefuroxime may help to reduce this risk, however sufficient concentrations, i.e. above the breakpoint (32 mg/L), are mandatory. The aim of this study is to evaluate the blood concentrations of cefuroxime during and after CABG surgery with cardiopulmonary bypass (CPB) and hypothermia, to determine the concentration of cefuroxime in sternum fluid and to evaluate possible factors of influence. METHODS: Seventeen patients were enrolled in this study, given 1.5 g cefuroxime at anaesthesia induction and an additional 1.5 g at start CPB. Blood samples were collected at skin incision, start CPB, every 30 min on CPB, end CPB, at wound closure and 1 h after surgery. Cefuroxime concentrations were determined by high performance liquid chromatography. RESULTS: In 47 % of the patients the cefuroxime concentration was below the breakpoint at some point during the operation and in 59 % of the patients 1 h after surgery. A statistically significant inverse correlation between estimated glomerular filtration rate and plasma cefuroxime concentrations was found (P = 0.034). Cefuroxime levels in the sternum are not significantly different from blood levels from the radial artery catheter, taken at approximately the same time (P = 0.30). CONCLUSIONS: The current antibiotic regimen used did not maintain cefuroxime concentrations above the breakpoint throughout the operation, suggesting insufficient antibiotic prophylaxis. Further research to other antibiotic regimes is therefore necessary.

Sympathetic activation markedly reduces endothelium-dependent, flow-mediated vasodilation.

OBJECTIVES: We sought to evaluate whether increased sympathetic outflow may interfere with flow-mediated dilation (FMD). BACKGROUND: Endothelial function, assessed as FMD, is frequently used as an intermediate end point in intervention studies. Many disease states with increased sympathetic tone are also characterized by endothelial dysfunction. METHODS: Sixteen healthy volunteers underwent FMD studies with and without concomitant sympathetic stimulation. Intra-arterial nitroglycerin (NTG) infusion was used to assess endothelium-independent vasodilation. Pathophysiologically relevant sympathetic stimulation was achieved by baroreceptor unloading, using a lower body negative pressure box. In a subset of eight volunteers, this protocol was repeated during loco-regional alpha-adrenergic blockade by intra-arterial infusion of phentolamine (PE). Reactive hyperemic flow was assessed with strain-gauge phlethysmography. RESULTS: Overall, FMD responses (8.3 +/- 3.4%) were significantly attenuated by concomitant sympathetic stimulation (3.6 +/- 3.4%, p < 0.01). Loco-regional alpha-adrenergic blockade had no effect on baseline FMD responses (10.7 +/- 4.7%), whereas the attenuation by sympathetic stimulation was abolished completely during PE co-infusion (11.5 +/- 3.3%). During intra-arterial NTG infusions, arterial diameters relative to baseline were not significantly different between the four possible stages. CONCLUSIONS: Sympathetic stimulation, at a clinically relevant range, significantly impairs the FMD response by an alpha-adrenergic mechanism.

Vascular Effects of ACE Inhibition Independent of the Renin-Angiotensin System in Hypertensive Renovascular Disease : A Randomized, Double-Blind, Crossover Trial.

-To evaluate whether ACE inhibition and angiotensin II type 1 blockade exert beneficial effects on NO availability independent of their blood pressure-lowering effect, we used a double-blind crossover design to study vascular function in 18 patients with hypertensive renovascular disease during 6 weeks of therapy with enalapril (Ena) and valsartan (Val) compared with non-renin-angiotensin system-mediated treatment with the alpha(1)-blocker doxazosin (Dox). Control measurements were performed in 13 age-matched volunteers. Forearm blood flow was assessed with venous occlusion plethysmography, and serotonin and nitroprusside were used as endothelium-dependent and -independent vasodilators, respectively. Blood pressure was similar during all treatment periods. Serotonin-induced vasodilation was decreased in patients during Dox treatment (n=12) compared with control subjects (n=13) (increase 42+/-20% versus 107+/-65%, P:<0.05). Crossover from Dox to Val (n=6) had no effect on serotonin response (increase 50+/-14%), but crossover to Ena (n=6) caused a significant improvement (increase 79+/-39%, P:<0.05 versus Dox). In an assessment of all patients, serotonin-induced vasodilation during Ena (n=12, increase 75+/-31%) was increased compared with both Val and Dox (43+/-14% and 42+/-20%, respectively; both P:<0.05 versus Ena). The nitroprusside response remained unaltered during all treatment periods. In conclusion, ACE inhibition improves the impaired endothelium-dependent vascular function in patients with hypertensive renovascular disease. This effect is unrelated to blood pressure-lowering or angiotensin II-mediated effects.

Selective ET(A) receptor antagonism with ABT-627 attenuates all renal effects of endothelin in humans.

++Endothelin (ET-1) acts as a potent vasoconstrictor in the human kidney, and this vasoconstriction could contribute to the ischemia seen in acute renal failure. In animal studies, the vasoactive properties of ET-1 are known to be ET(A) receptor-and/or ET(B) receptor-mediated; however, the receptor subtype involved in the human kidney remains to be defined. In a phase I, single-center, double-blind, randomized, three-period, crossover design, the effects of orally administered ABT-627, a selective ET(A) receptor antagonist, on renal hemodynamics during ET-1 infusion were evaluated. Two doses of ABT-627 (5 and 20 mg) were compared with placebo and nifedipine. For each dose level of ABT-627, a cohort of nine subjects was studied. A para-aminohippuric acid/inulin clearance test was performed once at the end of each 7-d treatment period. Infusion of ET-1 significantly decreased effective renal plasma flow, GFR, sodium excretion, and urine flow. Pretreatment with 20 mg of ABT-627 significantly decreased mean arterial pressure. In contrast, 7 d of treatment with both doses of ABT-627 did not affect baseline renal parameters. However, because mean arterial pressure decreased, a tendency toward a reduction of renal vascular resistance could indeed be demonstrated. Compared with placebo, both doses of ABT-627 were equally effective in blocking all renal effects caused by ET-1 infusion. In the model of exogenous ET-1 infusion, ABT-627 had a tendency to prevent ET-1-induced renal changes more effectively compared with nifedipine. The contribution of endogenous ET-1 and the ET(A) receptor in maintaining basal renal vascular tone in the human kidney is small. In addition, compared with placebo, selective ET(A) receptor antagonism with both doses of ABT-627 completely prevented all renal changes caused by ET-1 infusion.